One way for Microsoft to deal with consumer defections from PCs to mobile devices such as tablets and smartphones is to make sure its operating system is on as many of those devices as possible. Ubiquity has been a Microsoft (NASDAQ:MSFT) watchword, and it is a key accommodation in Windows 8, the cloud-based operating system that Microsoft released, in a test version, to consumers this week.

The test, or beta, version of Windows 8, called Consumer Preview, was unveiled at the Mobile World Congress trade show in Barcelona and is available for download from the company’s website. The release coincides with the opening of the Windows app store, whose applications will be available for free during the Consumer Preview period. It’s not yet clear when the system will be ready for final release, although it is likely to be included on a tablet that Hewlett-Packard (NYSE:HPQ) plans to release before the end of the year.

As noted in a post by Bloomberg Businessweek, Windows 8 is a major play for Microsoft, which has missed analyst estimates in four of the last five quarters, in part because consumers have migrated from PCs, where Microsoft Office is dominant, to mobile devices, where Google’s (NASDAQ:GOOG) Android operating system and Apple’s (NASDAQ:AAPL) iOS, for its iPhone, iPad, and iPod Touch devices, enjoy significant market share.

Windows 8 users, Bloomberg adds, have the option of signing in to a Windows account that lets them connect to their information stored in an Internet-based cloud on multiple personal computers and Windows Phones.